Starts at 31293264 and ends at 31453476 bp from pter ( according to hg19-Feb_2009) [Mapping TRPM1.png]

Note

TRPM1, the founding member of TRPM family was originally identified as melastatin 1 and accordingly all 8 family members are named TRPM (melastatin) (Montell et al., 2002). TRPM1 expression is restricted to the pigment cells of skin and eye. The protein encoded by this gene is similar to that of transient receptor potential (TRP) calcium channel family members. The protein expression is inversely correlated with melanoma aggressiveness, suggesting a role in melanoma metastasis.

DNA/RNA

Description

The TRPM1 gene consists of 27 exons, spans at least 58 kb genomic DNA, on chromosome 7 in mouse. In humans, the chromosomal localization of TRPM1 is on chromosome 15q13.3 region from 29080845 to 29181216 on the reverse strand. The TRPM1 gene encodes a 5.4kb (5428bp) mRNA transcript (Hunter et al., 1998; Fang and Setaluri, 2000). The promoter region of this gene contains 4 consensus binding sites for the microphthalmia-associated transcription factor (MITF), one of those binding site includes an M box, a motif shared by pigmentation genes (Hunter et al., 1998; Miller et al., 2004; Zhiqi et al., 2004). A 1-kb PvuII fragment from this region is capable of driving reporter gene expression in mouse and human melanoma cells.

Transcription

5.4 kb mRNA (full length transcript) with open reading frame of 4.812 (NT 129 to NT 4940, GenBank Accession No. NM_002420). Northern hybridization studies showed the presence of multiple short transcripts (1.8kb, 4kb, and 5.4kb) in human melanocytes as well as pigmented metastatic melanoma cell lines. However the full length mRNA is detectable only in melanocytes. (Fang and Setaluri, 2000).

Regulation of TRPM1: Short form of TRPM1 interacts directly and suppress the activity of full length form of TRPM1 (MLSN1-L), preventing its translocation to the plasma membrane (Xu et al., 2001), representing a mode of regulation of the channel activities. Presence of multiple isoforms of TRPM1 in normal melanocytes as well as pigment cell melanoma treated with a pharmacological agent suggests that TRPM1 can be regulated at the level of both transcription and mRNA processing (Fang and Setaluri, 2000). MITF is shown to be a major transcriptional regulator of TRPM1 expression through its interaction within the proximal promoter region (Miller et al., 2004; Zhiqi et al., 2004). Transfection of p53 or induction of endogenous p53 in melanocytes by ultraviolet (UV) radiation represses TRPM1 accompanied by decreased mobilization of intracellular Ca2+ and decreased extracellular Ca2+ uptake, indicating the role of p53 in TRPM1 regulation (Devi et al., 2007).

Description

TRPM1 is alternatively spliced and the splice variants are strongly depending on the cell type. Northern blot and RT-PCR analysis showed that the alternative splicing of TRPM1 mRNA produces short TRPM1 mRNAs derived from the 5' or 3' ends of the full length TRPM1. One of the major isoforms is predicted to encode a short protein (MLSN1-S) that includes only the N-terminal segment but not any transmembrane domain and is incapable of functioning independently as an ion channel.

Expression

TRPM1 is expressed exclusively in pigmented cells of the skin and the eyes.

Localisation

Isoforms of TRPM1 is mostly likely located on plasma membrane. Of the two major isoforms of TRPM1, L form (MLSN1-L) is localized on the cell membrane and the S form (MLSN1-S) is localized in the cytoplasm (Xu et al., 2001).

Function

TRPM1, transfected in heterologous HEK293T cells, acts as a calcium channel protein. The shorter isoform of TRPM1 has a regulatory effect on longer isoform, potentially suppresses the transport of longer isoform to cell membrane (Xu et al., 2001). Role of TRPM1 in cellular differentiation and proliferation was reported in human pigmented melanoma cell lines treated with hexamethylene bisacetamide (HMBA), were the expression of TRPM1 is upregulated (Fang and Setaluri, 2000). Lentiviral shRNA mediated knockdown of TRPM1 resulted in reduced intracellular Ca2+ and decreased Ca2+ uptake suggesting a role of TRPM1 in Ca2+ uptake by melanocytes (Devi et al., 2007).

Homology

Sequence similarity analysis revealed a limited homology to TRP family of calcium channel proteins and ~45% identity within the first 1200 amino acids of C.elegans (Prawitt et al., 2000).

Mutations

Note

Several single nucleotide polymorphisms have been identified but none of them is shown to be associated with any disease.

Identification and characterization of MTR1, a novel gene with homology to melastatin (MLSN1) and the trp gene family located in the BWS-WT2 critical region on chromosome 11p15.5 and showing allele-specific expression.